U.S. patent application number 14/195629 was filed with the patent office on 2015-09-03 for method and system for a lift device having independently steerable wheels.
The applicant listed for this patent is Xtreme Manufacturing, LLC. Invention is credited to Don Francis Ahern, Ronald Lee Fifield.
Application Number | 20150246684 14/195629 |
Document ID | / |
Family ID | 54006395 |
Filed Date | 2015-09-03 |
United States Patent
Application |
20150246684 |
Kind Code |
A1 |
Ahern; Don Francis ; et
al. |
September 3, 2015 |
METHOD AND SYSTEM FOR A LIFT DEVICE HAVING INDEPENDENTLY STEERABLE
WHEELS
Abstract
A system and method of controlling a scissors lift vehicle are
provided. The scissors lift vehicle system includes a carriage
including a plurality of independently steerable wheel assemblies
configured to engage a travel surface. The plurality of
independently steerable wheel assemblies, each steerable about a
steer axis of rotation include one of the plurality of wheel
assemblies being designated a master wheel and the remaining wheel
assemblies being designated slave wheels. The wheel assemblies each
include a variable-speed steer actuator configured to rotate a
respective wheel assembly about the steer axis of rotation of that
wheel assembly at a selectable rate. The wheel assemblies each also
include a wheel including a respective drive axis of rotation and a
variable-speed drive actuator configured to rotate that wheel about
a respective steer axis of rotation at a selectable rate.
Inventors: |
Ahern; Don Francis; (Las
Vegas, NV) ; Fifield; Ronald Lee; (Las Vegas,
NV) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xtreme Manufacturing, LLC |
Las Vegas |
NV |
US |
|
|
Family ID: |
54006395 |
Appl. No.: |
14/195629 |
Filed: |
March 3, 2014 |
Current U.S.
Class: |
701/41 ; 180/400;
180/413; 182/69.5 |
Current CPC
Class: |
B66F 11/042 20130101;
B62D 7/1509 20130101; B66F 17/006 20130101; B62D 6/001 20130101;
B62D 5/0418 20130101; B62D 5/0457 20130101 |
International
Class: |
B62D 5/04 20060101
B62D005/04; B62D 6/00 20060101 B62D006/00; B66F 11/04 20060101
B66F011/04 |
Claims
1. A scissors lift vehicle system comprising a carriage including a
plurality of independently steerable wheel assemblies configured to
engage a travel surface, said plurality of independently steerable
wheel assemblies, each steerable about a steer axis of rotation,
one of said wheel assemblies designated a master wheel, the
remaining wheel assemblies being designated slave wheels, said
wheel assemblies each comprising: a variable-speed steer actuator
configured to rotate said wheel assembly about the steer axis of
rotation at a selectable rate; a wheel comprising a respective
drive axis of rotation; a variable-speed drive actuator configured
to rotate said wheel about a respective steer axis of rotation at a
selectable rate.
2. The scissors lift vehicle system of claim 1, further comprising
a one or more processors coupled to one or more memory devices,
said one or more processors configured to: receive a steer input
from a user input device; generate a steer actuator speed command
signal based on the steer input; and transmit the speed command
signal to the variable-speed steer actuator of the designated
master wheel assembly.
3. The scissors lift vehicle system of claim 2, wherein said one or
more processors are further configured to generate a steer actuator
speed command signal that represents a maximum speed command signal
of the variable-speed steer actuator.
4. The scissors lift vehicle system of claim 2, wherein said one or
more processors are further configured to: receive a current
steering angle from each wheel assembly designated as a slave wheel
assembly; receive a current steering angle from the wheel assembly
designated as the master wheel assembly; generate a respective
steering angle target for each of each wheel assemblies designated
as a slave wheel assembly, the steering angle target based on the
received current steering angle from the master wheel assembly; and
transmit a respective steer actuator speed command to each slave
wheel assembly, the steer actuator speed command for each slave
wheel assembly based on the generated steering angle target for
that slave wheel assembly and the received current steering angle
from that slave wheel assembly.
5. The scissors lift vehicle system of claim 2, wherein said one or
more processors are further configured to generate a steer actuator
speed command signal that causes the master wheel assembly to turn
the master wheel at the maximum rate.
6. The scissors lift vehicle system of claim 2, wherein said
scissors lift vehicle system further comprises a steer mode
selector, said one or more processors are further configured to
receive a selection of a two-wheel steering mode or a four-wheel
steering mode.
7. The scissors lift vehicle system of claim 2, wherein said
scissors lift vehicle system further comprises a steer mode
selector, said one or more processors are further configured to
receive a selection of a crab steering mode.
8. The scissors lift vehicle system of claim 2, wherein said
scissors lift vehicle system further comprises a steer mode
selector, said one or more processors are further configured to:
receive a selection of a crab steering mode; receive a direction of
crab input; generate a steering angle command for the master wheel
assembly in the direction of the received direction of crab
movement; and generate a target steering angle command for the
slave wheels equal to a current steering angle of the master wheel
assembly.
9. The scissors lift vehicle system of claim 1, wherein each wheel
comprises a respective axle independent of an axle of any other
wheel.
10. The scissors lift vehicle system of claim 1, wherein said
linear drive device comprises a ball screw coupled to a steer
motor.
11. The scissors lift vehicle system of claim 1, further comprising
a steering angle position sensor associated with each steerable
wheel, said steering angle position sensor configured to detect a
relative angular position of the wheel and to generate a steering
angle position signal.
12. The scissors lift vehicle system of claim 11, further
comprising a user input device configured to receive a manual input
and generate a steering command signal, the steering command signal
and the steering angle position signal used to generate a linear
drive device speed signal.
13. A method of controlling a scissors lift vehicle, the scissors
lift vehicle including a plurality of wheel assemblies, the method
comprising: receiving a steer command from a user input device;
determining a first steering speed command for a first wheel
assembly based on the steer command, the first wheel assembly
independent of all other wheel assemblies; determining a target
steering angle for a second wheel assembly, the target steering
angle based on a current steering angle of the first wheel
assembly; determining a second steering speed command for the
second wheel assembly based on a difference between a current
steering angle of the second wheel assembly and the determined
target steering angle; and altering a course of travel of the
scissors lift vehicle using the first and second steering speed
commands.
14. The method of claim 13, further comprising determining a drive
speed command based on a current drive speed of the scissors lift
vehicle and a speed command.
15. The method of claim 14, wherein the scissors lift vehicle
includes a scissors stack assembly and a scissors stack height
sensor and wherein determining a drive speed command further
comprises determining the speed command based on the current speed
of the scissors lift vehicle, the speed command, and a scissors
stack height.
16. The method of claim 14, wherein determining a drive speed
command comprises determining a braking command for at lease some
of the plurality of wheel assemblies.
17. The method of claim 14, further comprising altering a speed of
travel of the scissors lift vehicle using at least one of friction
braking, dynamic braking, and regenerative braking based on the
braking command.
18. The method of claim 13, wherein the scissors lift vehicle
comprises a master wheel assembly and a plurality of slave wheel
assemblies, said method further comprising determining the second
steering speed command for each slave wheel based on a difference
between a current steering angle of the slave wheel assembly and a
respective target angle for that slave wheel assembly.
19. A scissors lift vehicle comprising: a carriage comprising a
plurality of independently steerable wheel assemblies, one wheel
designated as a master wheel assembly, a reminder of the wheel
assemblies designated as being slave wheel assemblies, each wheel
assembly comprising a wheel configured to engage a travel surface,
each wheel assembly comprising a steer axis of rotation, one of
said plurality of wheels positioned proximate each corner of said
carriage; a scissors stack assembly coupled to said carriage, said
scissors stack assembly comprising a plurality of scissors linkages
extendable from a retracted position, where said scissors linkages
are approximately horizontally configured to an extended position,
where said scissors linkages are approximately orthogonally
configured with respect to each other; a user input device
configured to generate a steer command; a steering angle position
sensor coupled to each independently steerable wheel assembly and
configured to generate a current steering angle position signal; a
processor communicatively coupled to a memory device, said memory
device including instructions that are executable by said
processor, said processor configured to: receive the steer command
from the user input device; generate a maximum speed steering rate
command for the master wheel assembly using the received steer
command; determine a target steering angle for each slave wheel
assembly based on a current steering angle of the master wheel
assembly; generate a steering rate command for each of the slave
wheel assemblies, the steering rate command proportional to a
difference between the determined target steering angle for each
slave wheel assembly and its current steering angle; and transmit a
respective generated steering rate command to each slave wheel
assembly.
20. The scissors lift vehicle of claim 19, said processor
configured to generate a maximum steering rate command for the
slave wheel assembly having the greatest difference between the
determined target steering angle for that slave wheel assembly and
its current steering angle.
Description
BACKGROUND
[0001] This description relates to lift devices, and, more
particularly, to mobile elevating work platform systems and methods
of controlling the operation of mobile elevating work
platforms.
[0002] Various types of mobile elevating work platforms have a lift
mechanism that can be moved in a vertical direction to bring a
worker close to otherwise inaccessible locations. The lift
mechanism is often mounted to a self-propelled carriage or chassis
having wheels for moving the platform between work areas. In one
type of mobile elevating work platforms, the lift mechanism to
achieve the vertical lift is often referred to as a "scissor lift,"
in which a plurality of linked, folding supports oriented in a
crisscross or "X" pattern in a "scissors stack." The upward motion
is achieved by the application of a force to a set of parallel
linkages, elongating the crossing pattern, and propelling the work
platform vertically. With the scissors stack mounted on the
carriage above the wheels, the wheels, steering configuration, and
propulsion configuration are typically a standard arrangement of
axles, wheels, linkage arms, and motors or drives. Such convention
steering limits the motion of the mobile work platform. For
example, a turn radius is limited and the ability to crab the
platform in a direction without turning it is virtually
non-existent.
[0003] Scissors lift devices are most useful if they are
self-propelled. Current scissor lift designs have many of the
propelling features mounted under the scissors lift assembly. A
hydraulic system, electrical system including batteries, and a
control system are also typically mounted on the carriage below the
scissors lift assembly. Additionally, axles, steering and
transmission components are also mounted on the carriage under the
scissors lift assembly. Accordingly, because of the equipment
located under the scissors lift assembly on the carriage, the
height of the work platform that carries a user to the work area is
greatly elevated above the floor surface. To gain access to the
work platform of known scissors lift assemblies, the user must
climb onto the platform, usually using several ladder steps
attached to the carriage and/or platform, and usually carrying
tools, equipment, and/or repair parts. Such access is dangerous and
laborious for the user. Moreover, mounting the scissors lift
assembly on top of the carriage increases the height of the
scissors lift vehicle when the scissors lift assembly is fully
retracted. The increased height limits areas that the scissors lift
vehicle can access.
BRIEF DESCRIPTION OF THE DISCLOSURE
[0004] In one aspect, a scissors lift vehicle includes a carriage
including a plurality of independently steerable wheel assemblies
configured to engage a travel surface. The plurality of
independently steerable wheel assemblies, each steerable about a
steer axis of rotation include one of the plurality of wheel
assemblies being designated a master wheel and the remaining wheel
assemblies being designated slave wheels. The wheel assemblies each
include a variable-speed steer actuator configured to rotate a
respective wheel assembly about the steer axis of rotation of that
wheel assembly at a selectable rate. The wheel assemblies each also
include a wheel including a respective drive axis of rotation and a
variable-speed drive actuator configured to rotate that wheel about
a respective steer axis of rotation at a selectable rate.
[0005] In another aspect, a method of controlling a scissors lift
vehicle includes receiving a steer command from a user input
device, determining a first steering speed command for a first
wheel assembly based on the steer command, the first wheel assembly
independent of all other wheel assemblies, and determining a target
steering angle for a second wheel assembly, the target steering
angle based on a current steering angle of the first wheel
assembly. The method further includes determining a second steering
speed command for the second wheel assembly based on a difference
between a current steering angle of the second wheel assembly and
the determined target steering angle, and altering a course of
travel of the scissors lift vehicle using the first and second
steering speed commands.
[0006] In yet another aspect, scissors lift vehicle includes a
carriage having a plurality of independently steerable wheel
assemblies wherein one wheel is designated as a master wheel
assembly and a reminder of the wheel assemblies are designated as
being slave wheel assemblies. Each wheel assembly includes a wheel
configured to engage a travel surface and a steer axis of rotation
where one of the plurality of wheels is positioned proximate each
corner of the carriage. The scissors lift vehicle also includes a
scissors stack assembly coupled to the carriage. The scissors stack
assembly includes a plurality of scissors linkages extendable from
a retracted position, where the scissors linkages are approximately
horizontally configured to an extended position, where the scissors
linkages are approximately orthogonally configured with respect to
each other. The scissors lift vehicle also includes a user input
device configured to generate a steer command, a steering angle
position sensor coupled to each independently steerable wheel
assembly and configured to generate a current steering angle
position signal, and a processor communicatively coupled to a
memory device that includes instructions that are executable by the
processor. The processor is configured to receive the steer command
from the user input device, generate a maximum speed steering rate
command for the master wheel assembly using the received steer
command, determine a target steering angle for each slave wheel
assembly based on a current steering angle of the master wheel
assembly, generate a steering rate command for each of the slave
wheel assemblies, the steering rate command proportional to a
difference between the determined target steering angle for each
slave wheel assembly and its current steering angle, and transmit a
respective generated steering rate command to each slave wheel
assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIGS. 1-13 show example embodiments of the method and
apparatus described herein.
[0008] FIG. 1 is a side elevation view of a scissors lift vehicle
in accordance with an example embodiment of the present
disclosure.
[0009] FIG. 2 is an exploded view of a linear steer guide assembly
that may be used with the scissors lift vehicle shown in FIG.
1.
[0010] FIG. 3 is a perspective view of the linear steer guide
assembly shown in FIG. 1 in an assembled state.
[0011] FIG. 4 is a perspective view of a wheel assembly shown in
FIG. 1 with a follower at an end of travel towards a second end,
which positions a wheel at approximately a 90.degree. angle with
respect to a reference representing the carriage shown in FIG.
1.
[0012] FIG. 5 is a perspective view of a wheel assembly 104 shown
in FIG. 1 with the follower at approximately mid-travel between the
first end and the second end, which centers the wheel with respect
to the carriage shown in FIG. 1.
[0013] FIG. 6 is a perspective view of a wheel assembly shown in
FIG. 1 with the follower at an end of travel towards the first end,
which positions the wheel at approximately a -60.degree. angle with
respect to the carriage shown in FIG. 1.
[0014] FIG. 7 is a schematic block diagram of a steering control
system used to control the wheel assemblies of the scissors lift
vehicle.
[0015] FIG. 8 is a plan view of the carriage shown in FIG. 1
illustrating a wide turn about a center point.
[0016] FIG. 9 is a plan view of the carriage shown in FIG. 1
illustrating a narrow turn about a center point.
[0017] FIG. 10 is a plan view of carriage shown in FIG. 1
illustrating a wide turn about a center point positioned abeam the
carriage.
[0018] FIG. 11 is a plan view of the carriage shown in FIG. 1
illustrating a narrow turn about a center point positioned closely
abeam the carriage.
[0019] FIG. 12 is a plan view of the carriage shown in FIG. 1
illustrating a crab movement of the carriage.
[0020] FIG. 13 is a flow diagram of a method of controlling the
scissors lift vehicle shown in FIG. 1 that includes a plurality of
wheel assemblies.
[0021] Although specific features of various embodiments may be
shown in some drawings and not in others, this is for convenience
only. Any feature of any drawing may be referenced and/or claimed
in combination with any feature of any other drawing.
[0022] Unless otherwise indicated, the drawings provided herein are
meant to illustrate features of embodiments of the disclosure.
These features are believed to be applicable in a wide variety of
systems comprising one or more embodiments of the disclosure. As
such, the drawings are not meant to include all conventional
features known by those of ordinary skill in the art to be required
for the practice of the embodiments disclosed herein.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0023] The following detailed description illustrates embodiments
of the disclosure by way of example and not by way of limitation.
It is contemplated that the disclosure has general application to
embodiments of a scissors lift vehicle and a method of operating a
scissors lift vehicle.
[0024] In the example embodiment, the scissors lift vehicle
includes a carriage comprising a plurality of independently
steerable wheels configured to engage a travel surface. The travel
surface could be any sufficiently smooth surface, which permits the
scissors lift vehicle to operate thereon, for example, but not
limited to an asphalt surface. Travel surface may be, for example,
concrete, wood, carpet, tile, or other surface in an indoor
application of the scissors lift vehicle. The wheels are configured
to rotate about an axle having a drive axis of rotation, the wheel
powered by a respective drive unit, such as, but not limited to an
electric drive motor coupled directly to the wheel or to the wheel
through a gear or transmission assembly. Typically, one wheel is
positioned at or near each corner of the rectangularly-shaped
carriage. The wheels are spaced as far as possible to improve the
stability of the scissors lift vehicle, especially when the
scissors stack assembly is extended. In various embodiments, more
than four wheels, one at each corner may be used. Additionally,
carriage may not be regularly-shaped, but may have other shapes,
where additional wheels could be used. The wheels may be spaced
apart in a fore/aft direction and in a right/left or athwartships
direction. At least some of the wheel assemblies are configured to
steer a respective wheel independently with respect to wheels
associated with a remainder of the plurality of wheel assemblies.
Some wheels may be steerable by their respective wheel assemblies,
some wheels may be fixed with respect to the carriage, and some
wheels may simply follow the carriage.
[0025] In various embodiments, the wheel assembly includes a linear
steer guide assembly. The linear guide assembly includes a linear
drive device configured to translate a follower along a linear
path. The linear drive device may be embodied in, for example, a
ball screw assembly or lead screw assembly coupled to a steer
motor, a hydraulic or pneumatic piston assembly, or other linear
driver. The linear guide assembly also includes a steering bracket
coupled to a wheel bracket. The wheel bracket is configured to
support the wheel associated with the respective wheel assembly.
The steering bracket includes a tab and is configured to rotate
about a steer axis of rotation. The linear guide assembly also
includes a steer link coupled between the follower and the tab, the
steer link is configured to rotate the steering bracket through the
tab using the linear motion of the follower. A steering angle
position sensor associated with each steerable wheel is configured
to detect a relative angular position of the wheel and to generate
a steering angle position signal. A user input device is configured
to receive a manual input from, for example, an operator, and to
generate a steering command signal. The user input device is
embodied in a single-axis input device, a two-axis, a keyboard,
switches, joystick, trackball, mouse, other input device, or
combinations thereof. In various embodiments, the steering command
signal and the steering angle position signal are used to generate
a wheel position command signal.
[0026] In the example embodiment, the scissors stack assembly
includes a plurality of scissors linkages extendable from a
retracted position, where the scissors linkages are approximately
horizontally configured to an extended position, where the scissors
linkages are approximately orthogonally configured with respect to
each other. The scissors stack assembly is pivotally coupled to the
base through a first pair of scissors linkages and is slidably
coupled to the base through a second pair of scissors linkages. The
base includes a slot configured to receive a pin. The base and the
first pair of scissors linkages are coupled in a pivotal joint. The
base and the second pair of scissors linkages are coupled in a
slidable joint using the slot and pin. The pivotal joint and the
slidable joint are located between the wheels spaced apart in the
right/left direction and within a profile of the wheels.
[0027] The scissors lift vehicle may also include a battery
compartment coupled to or formed in the carriage and that extends
between the fore and aft spaced wheels and is positioned outboard
of the scissors stack assembly. The battery compartment includes a
power source configured to supply a total electrical requirement of
the scissors lift vehicle. The scissors lift vehicle may include a
plurality of battery compartments. Each battery compartment is
located between the fore and aft wheels on each side of the
scissors lift vehicle. Typically, the power source is a battery. In
some embodiments, the power source may be embodied in an
engine.
[0028] Because some of the applications for the scissors lift
vehicle include lifting workers and their equipment in the interior
of buildings, the scissors lift vehicle size is limited to in an
athwartships direction to a distance that is less than typical door
openings. The width of typical door openings may vary by geographic
location, which would tend to dictate the desirable width of the
scissors lift vehicle.
[0029] The following description refers to the accompanying
drawings, in which, in the absence of a contrary representation,
the same numbers in different drawings represent similar
elements.
[0030] FIG. 1 is a side elevation view of a scissors lift vehicle
100 in accordance with an example embodiment of the present
disclosure. In the example embodiment, scissors lift vehicle 100
includes a carriage 102 that includes a plurality of independently
steerable wheel assemblies 104, each wheel assembly 104 includes a
respective wheel 105 configured to engage a travel surface 106
during operation of scissors lift vehicle 100. Travel surface 106
could be an asphalt surface in an outdoor application of scissors
lift vehicle 100 or may be concrete, wood, carpet, tile, or other
surface in an indoor application of scissors lift vehicle 100.
Wheels 105 are configured to rotate about a drive axis of rotation
108 and may be powered by a dedicated motor (not shown) coupled
directly to each wheel 105. Wheels include a circular profile
having a radius R and are spaced apart from each other along an
underside of carriage 102. Typically, one wheel assembly 104 is
positioned at or near each corner 110 of rectangularly-shaped
carriage 102. In various embodiments, wheel assemblies 104 are
spaced as far as possible to improve the stability of scissors lift
vehicle 100, especially when a scissors stack assembly 112 is
extended to lift a platform 113 to a working height. In various
embodiments, more than four wheels 105 are used. Additionally,
carriage 102 is not necessarily rectangularly-shaped, but may have
other shapes, where additional wheels 105 could be used. Wheels 105
are spaced apart in a fore/aft direction 114 and in a right/left or
athwartships direction (i.e., into or out of the page). Wheels 105
may be spaced from each other unequal distances apart, for example,
a track of the fore wheels may be wider or narrower than the track
of the aft wheels.
[0031] A base 116 is coupled to or formed with carriage 102 between
wheels 105 spaced apart in the right/left direction and is
positioned vertically such that base 116 lies within a profile of
wheels 105.
[0032] In the example embodiment, scissors stack assembly 112
includes a plurality of scissors linkages 118 pivotally coupled
together and extendable from a retracted position (shown in FIG.
1), to an extended position (not shown in FIG. 1).
[0033] FIG. 2 is an exploded view of a linear steer guide assembly
200 that may be used with scissors lift vehicle 100 (shown in FIG.
1). FIG. 3 is a perspective view of linear steer guide assembly 200
in an assembled state. In the example embodiment, linear steer
guide assembly 200 includes a linear drive device 202 configured to
translate a follower 204 along a linear path. In the example
embodiment, linear drive device 202 is a ball screw, however in
other embodiments a fluid cylinder or other linear driver may be
used. A steer rail 206 is used to guide follower 204 along the
linear path from a first end 208 of ball screw 202 to a second end
210 of ball screw 202. First end 208 is supported radially in a
motor end steer guide cap 212 using a ball bearing 214 and is
constrained axially using a thrust bearing assembly 215 including a
thrust bearing 216 and shims 218. A ball screw stop 220 provides a
surface for thrust bearing assembly 215 to engage between ball
screw 202 and motor end steer guide cap 212. Second end 210 is
supported radially in a fixed end steer guide cap 222 using a ball
bearing 224 and is constrained axially using a thrust bearing
assembly 226 including a thrust bearing 228 and shims 230. A ball
screw stop 232 provides a surface for thrust bearing assembly 226
to engage between ball screw 202 and fixed end steer guide cap
222.
[0034] A ball nut 234 engages threads 236 on ball screw 202. A
steer motor (not shown in FIG. 2 is coupled to first end 208 and
when energized, rotates ball screw 202 in a predetermined direction
to translate ball nut 234 in a desired direction. Ball nut 234 is
coupled to follower 204 causing follower 204 to be translated with
ball nut 234. Follower 204 rides along steer rail 206 using cam
followers 238 riding in a track 240.
[0035] FIG. 4 is a perspective view of a wheel assembly 104 (shown
in FIG. 1) with follower 204 at an end of travel towards second end
210, which positions wheel 105 at approximately a 90.degree. angle
with respect to a reference representing carriage 102 (shown in
FIG. 1). FIG. 5 is a perspective view of a wheel assembly 104
(shown in FIG. 1) with follower 204 at approximately mid-travel
between first end 208 and second end 210, which centers wheel 105
with respect to carriage 102 (shown in FIG. 1). FIG. 6 is a
perspective view of a wheel assembly 104 (shown in FIG. 1) with
follower 204 at an end of travel towards first end 208, which
positions wheel 105 at approximately a -60.degree. angle with
respect to carriage 102 (shown in FIG. 1).
[0036] A follower bracket 402 is coupled to follower 204. A
steering bracket 404 is coupled to a wheel bracket 406, which is
configured to support wheel 105 associated with wheel assembly 104.
Steering bracket 404 includes a tab 408 and is configured to rotate
about a steer axis of rotation 410. A steer link 412 is coupled
between follower bracket 402 and tab 408. Steer link 412 is
configured to rotate steering bracket 404 through tab 408 using
linear motion of follower 204.
[0037] In the example embodiment, linear drive device 202 is
coupled to a steer motor 414 through a gear box 416 or directly. A
steering angle position sensor 418 is associated with each
steerable wheel or with all wheels as needed. Steering angle
position sensor 418 is configured to detect a relative angular
position of wheel 105 and to generate a steering angle position
signal.
[0038] FIG. 7 is a schematic block diagram of a steering control
system 700 used to control wheel assemblies 104 of scissors lift
vehicle 100. In the example embodiment, steering control system 700
includes a main computer device 702 that is communicatively coupled
to a user input device 704, one or more steer controllers 706, and
one or more drive controllers 708. In the example embodiment, two
wheels 105 are driven and two wheels 105 free-wheel. In various
embodiments, all wheels 105 are driven wheels 105, each wheel 105
being associated with a respective drive controller 708. Main
computer device 702 is also communicatively coupled to a steering
angle position sensor 418 in each wheel 105. Each drive controller
708 is electrically coupled to a drive motor 710 associated with a
respective wheel 105. Each steer controller 706 is associated with
a respective steer motor 414 and gear box 416. In the example
embodiment, user input device 704 includes a joystick speed control
input 712, a right turn pushbutton 714, and a left turn pushbutton
716. Although illustrated as separate devices, main computer device
702, steer controllers 706, and drive controllers 708 may be
embodied in a single device.
[0039] During operation, speed in a forward or reverse direction is
controlled using joystick speed control input 712. Moving joystick
712 forward a selectable amount generates a speed command 718 that
is proportional to an amount of travel of joystick 712. In some
cases, the speed command may be constrained by other conditions of
scissors lift vehicle 100, for example, by an interlock or an
algorithm to prevent unsafe operation of scissors lift vehicle
100.
[0040] Pressing right turn pushbutton 714 starts a right turn
operation. One wheel 105 of all the wheels is designated as a
master wheel and the remaining wheels are designated as slave
wheels to the master wheel. Main computer generates a unique steer
command 720 for each wheel separately. Main computer 702 generates
a steer command for the master wheel that is either full on or full
off in a direction that rotates the master wheel toward a right
hand turn position. The master wheel is controlled using an
open-loop control scheme in that when right turn pushbutton 714 is
pressed, the master wheel begins turning towards a right turn
direction at full speed (i.e., steer motor 414 is commanded to
maximum RPM). When right turn pushbutton 714 is released, the
master wheel stops turning and maintains its current steering angle
(i.e., steer motor 414 is commanded to zero RPM). Each of the slave
wheel steering is controlled by a closed-loop control scheme. As
the master wheel is turning, main computer 702 then generates
respective steer commands for each of the slave wheels to maintain
synchronism with the master wheel. Each slave wheel is synchronized
with the master wheel by ensuring that each slave wheel is turning
about the same point on travel surface 106 as the master wheel.
[0041] Because each wheel may be starting the right turn operation
from a different steering angle, main computer 702 determines a
difference between each slave wheel starting steering angle to a
target turn angle. The slave wheel target turn angle is determined
based on the current steering angle of the master wheel. The slave
wheel target turn angle command may change while the current
steering angle of the master wheel changes during the right turn
operation. During the turn operation, main computer 702
continuously generates steering angle commands for each of the
slave wheels based on a current steering angle and the target
steering angle for that slave wheel. Main computer 702 also
attempts to achieve the turn as quickly as possible by determining
which slave wheel has the greatest difference between the current
steering angle and the target steering angle for that slave wheel.
The slave wheel having the greatest difference between its current
steering angle and its target steering angle is commanded to turn
at the greatest rate by commanding the respective steer motor 414
to its maximum speed. Steer motors 414 for the remaining slave
wheels are commanded to a speed that is proportional to the
difference between that wheel's current steering angle and its
target angle. When right turn pushbutton 714 is released, the
master wheel steer command stops the master wheel at the current
steering angle. A left turn operation performs in a similar
manner.
[0042] If joystick speed control input 712 is manipulated to
generate a speed command signal during a turn operation, a maximum
drive speed is determined by several factors and are reduced based
on any combination of a current chassis angle with respect to
level, a current platform height, and a current maximum steering
angle of any of the steerable wheels. The drive speed is fully
proportional to the user input with the maximum user input
corresponding to the determined maximum drive speed.
[0043] Scuffing of the drive wheels, when the wheels are steered
from center, is eliminated by reducing the drive speed of the drive
wheel corresponding to the inside wheel proportionally to the ratio
of the outside drive wheel turning radius to the inside drive wheel
turning radius.
[0044] In operation, a steering mode of operation is selected using
steering mode switch 713 and a direction of travel and speed are
input using user input device 704 embodied, in this case, in a
joystick for speed control and a right-turn pushbutton 714 and a
left-turn button 716. Pushing the handle of joystick 712 straight
forward commands scissors lift vehicle 100 to move straight forward
at a speed proportional to an amount of movement of user input
device 704.
[0045] Moreover, any of the wheels may include a brake (not shown)
that is used to facilitate braking scissors lift vehicle 100. The
brake may be embodied in a friction brake, a dynamic braking, a
regenerative brake, or combinations thereof. In various
embodiments, drive motor 710 is used for dynamic braking using
resistors to dissipate heat and/or regenerative braking by using
the momentum of scissors lift vehicle 100 in motion to generate
electrical power for charging energy storage devices (not shown),
such as, but not limited to batteries and/or supercapacitors.
[0046] FIG. 8 is a plan view of carriage 102 (shown in FIG. 1) of
scissors lift vehicle 100 (shown in FIG. 1) illustrating a turn
about a center point 802. In the example embodiment, scissors stack
assembly 112 and platform 113 are not shown for clarity. Carriage
102 includes a forward end 804 and an aft end 806. Forward end 804
includes a left wheel assembly 808 and a right wheel assembly 810.
Aft end 806 includes a left wheel assembly 812 and a right wheel
assembly 814. In the example embodiment, steering control system
700 operates in a two-wheel independent steering mode with wheel
assemblies 808 and 810 being steered and wheel assemblies 812 and
814 being fixed a zero steering angle. Although one of the wheel
assemblies is generally permanently designated as being the master
wheel, any one of left wheel assembly 808, right wheel assembly
810, left wheel assembly 812, and right wheel assembly 814 may be
designated as the master wheel. In such mode, the master wheel is
commanded to turn at the maximum rate (i.e., steer motor 414
operated at full speed in the proper direction). The slave wheel
receives from main computer 702 respective steer motor 414 speed
commands. The steer motor 414 speed commands for the slave wheels
cause the slave wheels to maintain synchronism with the master
wheel. The slave wheels are commanded to a target angle based on
center point 802, which is set using a turning radius of the master
wheel. Center point 802 may change position during the period that
the master wheel is turning, necessitating continuously changing
steer motor speed commands be determined and transmitted to slave
wheel steer motor 414. When right turn pushbutton 714 or left turn
button 716 is released, the master wheel stops turning and center
point 802 then becomes a fixed point about which the master wheel
is turning and the slave wheel steer motor speed commands will
reach zero RPM when the current steering angle of the slave wheel
match the target steering angle for the slave wheel. Accordingly,
each steerable wheel have a steering angle that puts the wheel
orthogonal to center point 802 and will travel in a direction
tangent to a circle having its center at center point 802 and a
radius equal to a distance from center point 802 to a steer axis of
rotation of each respective wheel. For example, wheel assembly 810
includes a wheel 816 having a steer axis of rotation 818 that
extends into and out of the page in this view. A radius 820 of a
turning circle 822 of wheel 816 about center point 802 is defined
between center point 802 and steer axis of rotation 818. A distance
824 of radius 820 defines a turn radius of wheel 816. Typically,
all four wheels of scissors lift vehicle 100 can have a different
steering angle for any given turn.
[0047] FIG. 9 is a plan view of carriage 102 (shown in FIG. 1) of
scissors lift vehicle 100 (shown in FIG. 1) illustrating a
two-steerable wheel turn about a center point 902. In the example
embodiment, scissors stack assembly 112 and platform 113 are not
shown for clarity. The operation of steering control system 700 for
this turn is similar to the operation described above with
reference to FIG. 8. Center point 902 is located proximate a steer
axis of rotation 904 of a wheel 906 of wheel assembly 814.
Accordingly, scissors lift vehicle 100 will essentially be turning
about wheel 906. To accomplish this turn, in the example
embodiment, wheel assembly 810 will be commanded to approximately a
+90.degree. angle with respect to carriage 102 and wheel assembly
808 will be commanded to approximately a +60.degree. angle with
respect to carriage 102. Wheel assembly 812 will be commanded to
approximately a 0.degree. angle with respect to carriage 102 as
illustrated in FIG. 5. The illustrated angles are examples only, as
the dimensions of scissors lift vehicle 100 may necessitate other
angles to accomplish the turns described herein.
[0048] FIG. 10 is a plan view of carriage 102 (shown in FIG. 1) of
scissors lift vehicle 100 (shown in FIG. 1) illustrating a
four-steerable wheel turn about a center point 1002. In the example
embodiment, scissors stack assembly 112 and platform 113 are not
shown for clarity. Center point 1002 is positioned off the
right-hand beam of carriage 102. To accomplish this turn, a master
wheel assembly, such as, wheel assembly 810 is commanded to turn at
a maximum rate by pressing right turn pushbutton 714. Each of wheel
assemblies 808, 812, and 814 are designated as slave wheels to
master wheel assembly 810. Main computer 702 synchronizes the
turning of wheel assemblies 808, 812, and 814 to that of master
wheel assembly 810. Main computer determines center point 1002
using the current steering angle of master wheel assembly 810 and
determines a target angle for each of wheel assemblies 808, 812,
and 814. Main computer then determines a steer motor speed command
for each of wheel assemblies 808, 812, and 814 based on a
difference between the current steering angle of wheel assemblies
808, 812, and 814 and their respective target angles. The wheel
assembly having the greatest difference is commanded to turn at
full speed and the other slave wheel assemblies are commanded to a
turn speed proportional to each slave wheel assembly difference
between its current steering angle and its respective target angle.
The steer motor speed command for each slave wheel assembly is
continuously updated based on changing conditions associated with
the master wheel assembly and/or scissors lift vehicle 100.
[0049] FIG. 11 is a plan view of carriage 102 (shown in FIG. 1) of
scissors lift vehicle 100 (shown in FIG. 1) illustrating a turn
about a center point 1102 positioned closely abeam carriage 102. In
the example embodiment, scissors stack assembly 112 and platform
113 are not shown for clarity. Center point 1002 is positioned just
off the right-hand beam of carriage 102.
[0050] FIG. 12 is a plan view of carriage 102 (shown in FIG. 1) of
scissors lift vehicle 100 (shown in FIG. 1) illustrating a crab
movement of carriage 102. In the example embodiment, scissors stack
assembly 112 and platform 113 are not shown for clarity. To
accomplish this movement, a crab mode of steering is selected and
user input device is manipulated to such that a master wheel
assembly is commanded by main computer 702 to a steering angle in
the direction of the crab movement. Main computer 702 generates a
slave wheel assembly target steering angle equal to the current
steering angle of the master wheel assembly. Each slave wheel
assembly achieves its respective target angle as described above.
In a crab movement, carriage 102 moves in a linear direction
selected without turning about a center point.
[0051] FIG. 13 is a flow diagram of a method 1300 of controlling
the scissors lift vehicle (shown in FIG. 1) that includes a
plurality of wheel assemblies. In the example embodiment, method
1300 includes receiving 1302 a steer command from a user input
device, determining 1304 a first steering speed command for a first
wheel assembly based on the steer command, the first wheel assembly
independent of all other wheel assemblies, and determining 1306 a
target steering angle for a second wheel assembly, the target
steering angle based on a current steering angle of the first wheel
assembly. Method 1300 also includes determining 1308 a second
steering speed command for the second wheel assembly based on a
difference between a current steering angle of the second wheel
assembly and the determined target steering angle and altering 1310
a course of travel of the scissors lift vehicle using the first and
second steering speed commands.
[0052] Optionally, wherein the scissors lift vehicle includes a
scissors stack assembly and a scissors stack height sensor, method
1300 includes determining the speed command based on the current
speed of the scissors lift vehicle and a scissors stack height.
Method 300 also optionally includes determining a point about which
the scissors lift vehicle will turn based on the received steer
command. Method 300 further optionally includes determining a
steering angle command for a wheel assembly that aligns an axis of
rotation of the wheel assembly with the determined point. Method
300 further optionally includes modifying at least one of a speed
of the scissors lift vehicle and a direction of travel of the
scissors lift vehicle comprises dynamically braking or
regeneratively braking at least some of the plurality of wheel
assemblies. Method 300 further optionally includes modifying at
least one of a speed of the scissors lift vehicle and a direction
of travel of the scissors lift vehicle comprises friction braking
at least some of the plurality of wheel assemblies. Method 300
further optionally includes modifying at least one of a speed of
the scissors lift vehicle and a direction of travel of the scissors
lift vehicle comprises applying friction braking to at least some
of the plurality of wheel assemblies using a bias member.
[0053] The process flows depicted in the figures do not require the
particular order shown, or sequential order, to achieve desirable
results. In addition, other steps may be provided, or steps may be
eliminated, from the described flows, and other components may be
added to, or removed from, the described systems. Accordingly,
other embodiments are within the scope of the following claims.
[0054] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as "about" and
"substantially", are not to be limited to the precise value
specified. In at least some instances, the approximating language
may correspond to the precision of an instrument for measuring the
value. Here and throughout the specification and claims, range
limitations may be combined and/or interchanged, such ranges are
identified and include all the sub-ranges contained therein unless
context or language indicates otherwise.
[0055] The above-described embodiments of a method and system of a
scissors lift vehicle provide a cost-effective and reliable means
of lifting workers to an elevated work site. More specifically, the
methods and systems described herein facilitate a worker's ingress
and egress to a work platform coupled to a scissors lift assembly
portion of the scissors lift vehicle. In addition, the
above-described methods and systems facilitate accessing narrow
portals to work areas. As a result, the methods and systems
described herein facilitate worker safety and work site access in a
cost-effective and reliable manner.
[0056] This written description uses examples to describe the
disclosure, including the best mode, and also to enable any person
skilled in the art to practice the disclosure, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the disclosure is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *